Method for leaching nickeliferous laterite ores

Abstract

A process is provided for the leaching of both the "limonite" (Fe approx. >=25% and Mg approx. >=6%) and "saprolite" (Fe approx. <=20% and Mg approx. >=10%) fractions of typical nickel and cobalt bearing laterite ore. The low magnesium fraction of the laterite ore is leached with sulfuric acid at high pressure and temperature to solubilize the metal values while precipitating most of the solubilized iron as hematite or other iron compounds and a portion of the dissolved aluminum as alunite or other aluminum compounds. After reducing the pressure of the leach slurry to approximately atmospheric pressure, the pregnant leach slurry or solution is contacted with the high magnesium fraction of the ore to solubilize most of the nickel contained in the high-magnesium ore fraction while dissolving only a small portion of the iron content of the high magnesium ore fraction. Further neutralization of the leach slurry in the presence of an alkali metal or ammonium ion will allow the precipitation of iron-bearing jarosite at ambient pressure. This process for incorporating the leaching of saprolite in the high pressure leaching process for limonite ores requires neither high temperature and pressure, nor special treatment of the saprolite ore fraction, nor the addition of special reagents, e.g. reducing reagents.

What is claimed:  
     
       1. A hydrometallurgical sulfuric acid leaching process for the extraction of nickel and cobalt from nickeliferous laterite oxide ore that comprises: 
       a. providing an aqueous pulp of nickeliferous oxide ore with a low magnesium content;  
       b. leaching the aqueous pulp at a temperature of at least about 200° C. and at an elevated pressure with an addition of sulfuric acid at least sufficient stoichiometrically to effect the leaching of contained nickel and cobalt and thereby provide a leach liquor discharge of nickel sulfate, cobalt sulfate and a leach residue, wherein the leach liquor contains between 76 and 114 g/L of sulfuric acid;  
       c. adding controlled quantities of a raw, high magnesium containing nickeliferous oxide ore to the leach liquor from step (b) at atmospheric pressure to yield a final neutralization slurry, wherein  
       (i) the raw ore is added at temperatures of from 80° C. up to the atmospheric pressure boiling point of the final neutralization slurry,  
       (ii) sufficient agitation and time are provided to effect the extraction of nickel and cobalt from the raw ore, wherein between 73 and 94% of the nickel present in the nickeliferous laterite oxide ore is extracted, and  
       (iii) a reducing agent is not added to the final neutralization slurry to control its oxidation/reduction potential; and  
       d. adding a sufficient amount of a precipitating agent selected from the group consisting of alkali metal ions, ammonium ions, and mixtures thereof, to the pulp of step (a), leach liquor of step (b), or final neutralization slurry of step (c) to precipitate ferric iron as jarosite.  
     
     
       2. The process of  claim 1  wherein the leach liquor and leach residue of step (b) are not separated before step (c). 
     
     
       3. The process of  claim 1 , further comprising leaching a portion of the raw, high magnesium containing nickeliferous oxide ore at atmospheric pressure with sulfuric acid before adding the raw ore to the leach liquor of step (b). 
     
     
       4. The process of  claim 1  further comprising adding to the final neutralization slurry a neutralization agent selected from the group consisting of alkali and alkaline earth oxides, hydroxides, carbonates, and mixtures thereof. 
     
     
       5. The process of  claim 1  further comprising subjecting the final neutralization slurry to a solid/liquid separation step to produce a final pregnant leach liquor suitable for recovery of nickel and cobalt and a final leach residue. 
     
     
       6. The process of  claim 1  further comprising grinding the raw, high magnesium containing nickeliferous oxide ore before adding the raw ore to the leach liquor of step (b). 
     
     
       7. The process of  claim 1 , wherein the leach liquor of step (b) contains between 92 g/L and 114 g/L of sulfuric acid. 
     
     
       8. The process of  claim 1 , wherein the leach liquor of step (b) contains between 102 g/L and 114 g/L of sulfuric acid. 
     
     
       9. The process of  claim 1 , wherein the pH of the final neutralization slurry is not controlled during addition of the raw, high magnesium containing nickeliferous ore. 
     
     
       10. A process for the extraction of nickel and cobalt from nickeliferous laterite oxide ore that comprises sequentially: 
       a. providing an aqueous pulp of nickeliferous oxide ore with a low magnesium content;  
       b. leaching the aqueous pulp at a temperature of at least 200° C. and at a pressure above atmospheric with an amount of sulfuric acid at least stoichiometrically sufficient to leach contained nickel and cobalt to provide an above atmospheric pressure leach liquor of nickel sulfate, cobalt sulfate, and a leach residue, wherein the leach liquor contains between 76 and 114 g/L of sulfuric acid;  
       c. discharging the above atmospheric pressure leach liquor comprising nickel sulfate, cobalt sulfate, acid, and a leach residue from step (b) to atmospheric pressure;  
       d. adding a raw, untreated high magnesium containing nickeliferous oxide ore and additional sulfuric acid to the atmospheric pressure leach liquor from step (c) to yield a final neutralization slurry, wherein  
       (i) the raw ore and additional sulfuric acid are added at temperatures of from 80° C. up to the atmospheric pressure boiling point of the final neutralization slurry,  
       (ii) sufficient agitation and time are provided to effect the extraction of nickel and cobalt from the raw ore, wherein between 73 and 94% of the nickel present in the nickeliferous laterite oxide ore is extracted, and  
       (iii) a sufficient amount of a precipitating agent selected from the group consisting of alkali metal ions, ammonium ions, and mixtures thereof, is added to the pulp of step (a), leach liquor of step (c), or final neutralization slurry of step (d) to precipitate ferric iron as jarosites;  
       e. adding a neutralization agent selected from the group consisting of alkali and alkaline earth oxides, hydroxides, carbonates, and mixtures thereof to the final neutralization slurry of step (d) to yield a neutralized leach slurry; and,  
       f. subjecting the neutralized leach slurry to a solid/liquid separation step to produce a final pregnant leach liquor suitable for recovery of nickel and cobalt and a final leach residue.  
     
     
       11. The process of  claim 10 , wherein the leach liquor and leach residue of step (b) are not separated before step (d). 
     
     
       12. The process of  claim 10 , wherein the leach liquor of step (b) contains between 92 g/L and 114 g/L of sulfuric acid. 
     
     
       13. The process of  claim 10 , wherein the leach liquor of step (b) contains between 102 g/L and 114 g/L of sulfuric acid. 
     
     
       14. The process of  claim 10 , wherein a reducing agent is not added to the final neutralization slurry to control the oxidation/reduction potential. 
     
     
       15. The process of  claim 10 , wherein the pH of the final neutralization slurry is not controlled during addition of the raw, high magnesium containing nickeliferous ore. 
     
     
       16. A process for the extraction of nickel and cobalt from nickeliferous laterite oxide ore that comprises sequentially; 
       a. providing an aqueous pulp of nickeliferous oxide ore with a low magnesium content;  
       b. leaching the aqueous pulp at a temperature of at least 200° C. and at a pressure above atmospheric with an amount of sulfuric acid at least stoichiometrically sufficient to effect the leaching of contained nickel and cobalt to provide an above atmospheric pressure leach liquor of nickel sulfate, cobalt sulfate, and a leach residue, wherein the leach liquor contains between 76 and 114 g/L of sulfuric acid;  
       c. discharging the above atmospheric pressure leach liquor comprising nickel sulfate, cobalt sulfate, acid, and a leach residue from step (b) to atmospheric pressure;  
       d. then adding a raw, untreated high magnesium containing nickeliferous oxide ore and optionally adding additional sulfuric acid to the atmospheric pressure leach liquor from step (c) to yield a final neutralization slurry, wherein  
       (i) the raw ore and optional sulfuric acid are added at temperatures of from 80° C. up to the atmospheric pressure boiling point of the final neutralization slurry,  
       (ii) sufficient agitation and time are provided to effect the extraction of nickel and cobalt from the raw ore, wherein between 73 and 94% of the nickel present in the nickeliferous laterite oxide ore is extracted, and  
       (iii) a reducing agent is not added to the final neutralization slurry to control its oxidation/reduction potential;  
       e. adding a sufficient amount of a precipitating agent selected from the group consisting of alkali metal ions, ammonium ions, and mixtures thereof, to the final neutralization slurry of step (d) to precipitate ferric iron as jarosites; and,  
       f. subjecting the slurry from step (e) to a solid/liquid separation step to produce a final pregnant leach liquor suitable for recovery of nickel and cobalt and a final leach residue.  
     
     
       17. The process of  claim 16 , wherein the leach liquor and leach residue of step (b) are not separated before step (d). 
     
     
       18. The process of  claim 16 , wherein the leach liquor of step (b) contains between 92 g/L and 114 g/L of sulfuric acid. 
     
     
       19. The process of  claim 16 , wherein the leach liquor of step (b) contains between 102 g/L and 114 g/L of sulfuric acid. 
     
     
       20. The process of  claim 16 , wherein the pH of the final neutralization slurry is not controlled during addition of the raw, high magnesium containing nickeliferous ore.